1. Field of the Invention
The present invention relates to an illuminator, and, more particularly, to an illuminator that can be applied to a backlighting source device of a display panel employing a ferroelectric liquid crystal.
2. Related Background Art
In a liquid crystal display panel, an irregular-reflection plate is disposed on the back surface of the panel and electro-optical modulation is identified by using a light reflected thereform, or an illuminator is disposed on the back surface and light rays from the back surface are controlled by the switching operation of a liquid crystal, so that the display can be identified. In general, the former is called a reflective type liquid crystal display panel, and the latter, a transmissive type liquid crystal display panel. The reflective type liquid crystal display panels and transmissive type liquid crystal display panels have advantages respectively inherent therein. Particularly the transmissive type liquid crystal display panels are suited for their application in display units of office instruments.
The transmissive type liquid crystal display panels have hitherto employed an illuminator as illustrated in FIG. 13. More specifically, in FIG. 13, a panel is so constituted that light rays from two light sources 1301 and 1302 may be totally reflected on each of a surface-reflection surface 1304 and a minute prism reflection surface 1305 in a transparent light-transmitting member 1303, thereafter being transmitted through the surface-reflection surface 1304 and through a light-scattering member 1306, and being converted into scattered light there, so that a liquid crystal display panel 1307 can be illuminated from its back surface. The numeral 1308 denotes a housing that supports the light source 1301, the light-transmitting member 1303 and so forth. The liquid crystal display panel 1307 is provided, on its top and bottom, with two sheets of polarizers, which, however, are not shown in the drawing. Driving circuit boards, fixing members or the like to be connected to the liquid crystal display panel 1307 are also omitted (The same applies herein).
However, in an illuminator 1300 employing such a light-transmitting member 1303, there have been several problems. For example, beams from the light-sources 1301 and 1302 can be utilized at a low rate, and hence a large electric power to be consumed is required in order to brightly illuminate the liquid crystal display panel 1307; moreover, since lights from the light-sources 1301 and 1302 spread in a radial form, the lights are transmitted from the light-transmitting member 1303 in a large amount in the vicinity of the light-sources 1301 and 1302; and the lights are transmitted from the light-transmitting member 1303 in a small amount at a position distant from the light-sources 1301 and 1302, thus making it difficult to effect uniform surface illumination.
For these reasons, conventionally used has been an illuminator as illustrated in FIG. 14. This illuminator is of the twin-lamp type in which light sources and light-transmitting members are disposed one by one on the right and the left. Because of symmetrical positional relationship and the same functions, description will be made below only of light-source 1401-1 and a light-transmitting member 1402-1 which are located on one side. More specifically, in FIG. 14, the numeral 1402-1 denotes the light-transmitting member having the structure that a number of transparent sheet-like members 1407 formed of, for example, polymethyl methacrylate (PMMA) or glass sheets are laminated to each other with use of an adhesive or the like. They are laminated interposing an air layer, or an adhesive layer having a smaller refractive index than PMMA, in order to prevent crosstalk between the transparent sheet-like members. Also, the numeral 1403-1 denotes a light-reflecting member comprised of, for example, a film having a mirror surface, which member is so disposed as to surround the circumference of the light source 1401-1 so that the beams can be utilized at a high rate. Part A of light rays emitted from the light-source 1401-1 travels directly to the light-transmitting member 1402-1, propagates through the transparent sheet-like member 1407 from one end thereof while repeating the total reflection, exits from the other end of the transparent sheet-like materials 1407, reflected on the surface of the light-reflecting member 1403-3, passes through a light-scattering member 1404, and is converted into scattered light there, thus illuminating a liquid crystal display panel 1405 from its back surface. Another part B of the light rays reaches the reflection surface of the light-reflecting member 1403-1, and, after it is reflected there, returns again to the surface of the light-source 1401-1, and then passes through its inside and exits through the surface of the opposite side, and comes in the light-transmitting member 1402-1 as shown by B. In a final stage, this light ray also exits from the light-scattering member 1404. In other words, the light rays that have substantially equally travelled through the light-transmitting member 1402-1 from an end thereof and exit through the bottom end in such a state that the light intensity is retained, and are reflected and with scattered so that there can be obtained uniform surface illumination. Thus, the illuminator 1400 shown in FIG. 14 has been particularly useful for uniform illumination of large liquid crystal display panels when used with the increased numbers of the transparent sheet-like members 1407 in the light-transmitting member 1402-1.
To solve the problems in the illuminator illustrated in FIG. 13, an illuminator as illustrated in FIG. 15 is also used.
In FIG. 15, a light-reflecting member 1502 comprises, for example, a film having a mirror surface, and, in order to increase the utilization rate of beams, disposed on the inner wall of a housing 1505 in such a manner that it may surround light-sources 1501. The numeral 1503 denotes a light screen comprising, for example, a polyester film on which opaque materials are provided in the form of dots by vapor deposition or printing, and density distribution is formed on the part of the dot-like opaque materials so that the beams that come in the light screen may be brought into outgoing beams having uniform light distribution.
Part A of light rays emitted from the light-sources 1501 directly reaches and passes through the light screen 1503, and is converted into scattered light through a light-scattering member 1504, thus illuminating a liquid crystal display panel 1506 from its back surface. Another part B of the above light rays is reflected on the light-reflecting member 1502, and thereafter reaches the light screen 1503, and, in a final stage, this light ray B is also converted into scattered light through the light-scattering member 1504 and then outgone. The light rays emitted from the light sources 1501 may spread in a radial form around the light sources 1501, and the beams reaching the light screen 1503 may have different densities depending on the position of the surface at which beams come in the light screen 1503. Accordingly, forming the density distribution on the part of the opaque materials provided on the light screen 1503 makes uniform the density of the beams coming in the light-scattering member 1504, so that there can be obtained a surface light source free of non-uniformity in luminance. This illuminator also enables utilization of almost all of the light rays except that a part of light rays emitted from the light sources is intercepted at the opaque materials on the light screen 1503, thus making it possible to obtain a highly luminous surface light source. Moreover, a surface light source having a large area can be obtained by increasing the number of the light-sources 1501, and hence this illuminator has been useful for backlighting sources of large liquid crystal display panels.
Incidentally, the ferroelectric liquid crystal display panel described in U.S. Pat. No. 4,367,924 issued to Clark et al. enables liquid crystal display with a large area, but experiments made by the present inventors revealed that the alignment disturbance (hereinafter referred to as "sanded texture") that may undoubtedly cause a switching failure has been produced as a result of a drop impact test carried out as reported below after the ferroelectric liquid crystal display panel is fixed on the illuminators of FIG. 14 and FIG. 15 each.
Moreover, conventional illuminators, in which a light-transmitting member is required to be obliquely fixed at a given angle to the bottom surface of a housing and to a light-scattering member, have had the problems such that they require a member with which the light-transmitting member is pressed at its top surface and fixed, and assembly performance becomes poorer with an increase in the number of parts.